The field of this invention is polybromide resins for use in disinfecting water. The preparation and use of such resin disinfectants are described in prior patents (see, for example, U.S. Pat. Nos. 3,316,173, 3,436,345, and 3,462,363), and have been in commercial use for a number years as disinfectants for potable water. Everpure, Inc. of Westmont, Ill. markets bromination systems for treating drinking water in marine applications, such as ships, submarines, and offshore oil well drilling rigs. The disinfecting agent is a strong base anion exchange resin in bromide form loaded with bromine. When water is passed through the bed of the resin beads, which are contained in disposable cartridges, bromine (Br.sub.2) is released into the water.
In prior art commercial practice, beads of quaternary ammonium anion exchange resin are usually converter from a chloride form to a bromide form, and are loaded with elemental bromine in the form of a polybromide complex (Br.sub.n). The number of bromines in the polybromide complex "n" can be 3, 5, or 7, representing, respectively, tribromide (Br.sub.3), pentabromide (Br.sub.5), and heptabromide (Br.sub.7). The loading of the resin is carried out in an aqueous slurry, in which the water phase contains a bromide salt (e.g., sodium bromide) and elemental bromine. After the resin beads have been loaded with the bromine, it has been the practice to drain and aspirate the beads to remove external water, while leaving the beads internally in moist condition. The beads have then been packaged in sealed cartridges for shipment, storage, and use in the marine applications referred to above.
Commercial brominating cartridges prepared as described have been found to have two disadvantages in use. When they are stored for a number of months or years, as may be required in marine applications, the effective bromine content of the resin continually decreases, and may reach such a low level that the needed amount of bromine is not released into the water during use. Ideally, the resin beads should release bromine at a controlled and predeterminable level for use in a proportioning systems where the bromine is picked up by a side stream, and then combined in predetermined proportions with the main stream of water to be treated. It has been found that the resin cartridges after long storage may not provide the desired predetermined release rate, and, after long storage, the bromine content of the cartridge may have been reduced to such a low level that the cartridges cannot be effectively used at all. Such loaded resin deterioration is particularly noticeable with storage under relatively warm conditions, such as temperatures from 80.degree. to 100.degree. F.
Another disadvantage encountered in field use of the brominating cartridges is that of an initially undesirably high rate of release of bromine. This usually occurs during passage of the first several hundred gallons of water through the cartridges. Excess bromination of the water can result, and such a high release rate can be misleading to the users. For example, if the bromination system is adjusted to proportion with respect to the initial high rate of release, when the release rate drops to the lower level of sustained release it may be assumed that the cartridge has ceased to perform satisfactorily and should be discarded. Actually, it is the lower sustained release rate which is employed for long-term use of the cartridge. For example, a cartridge containing 1.25 kilograms of resin can be sufficient to feed 1 part per million of bromine to 200,000 liters of water.